Melt butter in saucepan.
Add sugar and cocoa. Mix well. Allow mixture to cool.
Whisk egg with vanilla. Whisk into cooled butter mixture.
Add graham crackers, coconut and walnuts.
Press evenly into greased 9 x 9 square pan.
Chill for at least 20 minutes.
Whip butter. Add in custard powder and milk.
Gradually add in sugar, flavouring and food colour.
Spread over base with spatula and return to the fridge.
Melt chocolate and butter over water bath. Remove and cool down.
Add on top of the filling layer. Spread with spatula to get even layer.
Return to fridge for another 15 minutes.
Cut into squares and serve.